D.c. motor speed control and signalling system, particularly designed for motion picture cameras



March 9, 1965 LANK F. A. B D.C. MOTOR SPEED CONTROL AND SIGNALLINGSYSTEM, PARTICULARLY DESIGNED FOR MOTION PICTURE CAMERAS Original FiledDec. 14, 1956 FILM TRANSPORT MECHANISM OF CAMERA United States PatentD.C. MOTOR SPEED CONTROL AND SIGNALLING SYSTEM, PARTICULARLY DESIGNEDFOR MO- TIQN PICTURE CAMERAS Fritz A. Blank, New Rochelle, N.Y.,assignor, by direct and mesne assignments, of one-half to A. KipLivingston, West Hempstcad, N.Y., and one-half to Longines- WittnauerWatch Co., Inc, New Yorir, N.Y., a corpo ration of New York Originalapplication Dec. 14, 1956, Ser. No. 628,233, new Patent No. 2,971,432,dated Feb. 14, 1961. Divided and this application Dec. 19, 196i), Ser.No. 76,783

\ 4 Claims. (Cl. 318--325) This invention relates to direct currentmotor speed controlling means and motor speed signalling systems and,more particularly, to an improvement in electric battery powered motionpicture cameras, such as apparatus combining camera motor speedregulation with a visual signal indication whenever the operating speedof the camera mechanism falls below a predetermined critical speed, dueto depletion of the operating battery or for any other reason.

The invention may be adapted to any motion picture camera in which themechanism is driven by an electric motor deriving its motivating powerfrom a battery source. Gne example of such a camera, having aself-contained battery source, is disclosed in the co-pendingapplication of John W. Oxberry, Serial No. 405,543 filed January 22,1954, now Patent 2,912,898, issued November 17, 1959.

In the art of taking motion pictures it is necessary that the speed ofoperation of the camera shutter and film transport mechanism be wellregulated, within tolerable limits, in order that the pictures whenprojected will be free from flicker, and in order that the apparentmotion of the projected images will be smooth and not jerky. In batteryoperated motion picture cameras it is not only necessary to maintain thespeed of a direct current motor substantially constant-within a narrowrange of limited speed variations, which range is the optimum speed fornormal operation, but it also becomes necessary to provide warning meansto signal the camera operator whenever the potential of the operatingbattery source is decreased to a point at which the battery sourcebecomes inadequate to maintain the required speed of motor operation.Such a decrease in battery potential may result from battery depletionthrough prolonged use, from normal shelf deterioration, from excessivetemperature changes, or through other causes beyond the knowledge orcontrol of the operator. If the depleted batteries are not removed andreplaced when this condition arises, the camera may continue to operatebut at a speed below the desired optimum speed, with a resultantdeterioration in the quality of motion pictures which may be projectedfrom the exposed and developed film.

Although the camera batteries in normal operation may continue to supplythe requisite energy for several hundred hours, batteries do have alimited shelf life and the occasional and sometimes infrequent use ofcameras in the taking of home movies affords the operator no reliableguide as to when fresh batteries should be installed.

One of the objects of the present invention is to provide visual signalmeans for informing an operator of battery powered motor-drivenequipment when new batteries should be installed in the supply circuitof the motor, such as for example the operator of a battery poweredmotion picture camera.

Another object is to provide such a signal which is visible within thecamera view finder, whereby an opera tor may be immediately informed ofany decrease in camera motor speed while the camera is in use.

A further object is to provide visual signal means within the viewfinder which will give a signal of one character to warn of anaproaching decrease in motor speed before a critical minimum speed isreached, and which will give a signal of different characteristic whenthe motor is reduced below the critical minimum speed.

Another object is to provide visual signal means within an electricallyoperated camera visually to indicate by a first characteristic when thecamera is operating properly, and to indicate by a differentcharacteristic when the camera is operating at an improper speed.

A more general object is to provide improved direct current motor speedregulation with visual indication of speed changes within predeterminedlimits, suitable for use in various DC. motor-driven equipment, such asa battery operated motion picture camera.

A more specific object is to combine motor speed control means withelectrical signal control means in a battery operated motion picturecamera to produce a visual signal, in the camera View finder, wheneverthe motor speed drops below a predetermined critical speed.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the combinations of elements, andarrangement of parts, which will be exemplified in the constructionshereinafter set forth, and the scope of the invention will be indicatedin the claims.

For a fuller understanding of the nature and objects of the inventionreference should be had to the following detailed description taken inconnection with the accompanying drawings, in which:

PEG. 1 is a schematic diagram of speed and signal controlling means andcircuit thereof according to one embodiment of the invention; and

FIG. 2 is a schematic diagram of an alternative form of a signal controland circuit thereof according to the invention.

Prior to the present invention there was no satisfactory way for theoperators of battery powered home movie cameras to determine when theyshould replace the camera operating battery. Because the electric motorsof these cameras operate so smoothly and quietly, and for such a longperiod of time before the batteries become depleted, it required anextremely acute sense of hearing to detect a slight reduction in cameraoperating speed such as might cause a deterioration in the quality ofmotion pictures filmed. Very often the need to replace batteries mightnot be detected until after a complete roll of film had been exposed,developed and projected. To eliminate this possibility of unknowinglyexposing a roll of film at an improper speed, due to depletion of thecamera battery, I have devised the motor speed control and visual signalmeans of the present invention to assure the operator that and when hiscamera is functioning at the proper speed, and to warn him instantlywhen the camera motor speed starts to decrease below a permissiblelimit.

Referring now in greater detail to the drawings, a visual signalindicating element 9 is introduced into the view finder enclosure. Inthe preferred embodiment of the invention the visual signal indicatingelement comprises an electric lamp 9, although it is to be understoodthat other forms of visual indicators may be employed within the scopeof the invention.

Referring to FIG. 1, an electric motor It drives the camera shutter andfilm transport mechanism (not shown) through worm gear 11 mounted on thelower end of motor shaft 12. On the opposite or top end of motor shaft12 is mounted a fly-ball speed control governor indicated generally at15, the detailed structure of which will be described more fullyhereinafter.

Mounted on the end casing of motor 10 is a generally U-shaped bracket(not shown) which carries on one leg thereof an insulating member (alsonot shown), to the upper end of which is mounted an adjustableelectrical contact member 20. A second electrical contact member 21 ismounted adjacent to but below contact 20, also oeing supported by theinsulating member. The insulated mounting (not shown) supports a pair ofsubstantially parallel spring contact members 26 and 27 which, asindicated, are insulated from each other. The opposite ends of springmembers 26 and 27 carry movable electrical contacts 28 and 29 which whenthe electric motor is idle are normally in conductive engagement withthe abutting electrical contacts 2%) and 21. Slidably mounted on theupper end of motor shaft 12 in a position to be operable by fly-ballgovernor is a plunger 30 of insulating material adapted to engage andoperate upon spring contact member 27 when motor 10 is in operation.Between the spring members 26 and 27 is positioned an insulating pin 31adapted to engage and operate upon spring 26 after spring 27 is flexedby operation of plunger 30.

A 4-element leaf spring electrical switch, indicated generally at 40, isprovided comprising four contact members 41, 42, 43 and 44. Switchsprings 41, 42 and 43 are insulated from each other and from the motorcasing 10 by laminations of insulating material 45. An external switchbutton (not shown) is slidably mounted on the camera casing in aposition to engage behind the lower extremity of switch spring member44. In FIG. 1, which is a schematic diagram of a preferred embodiment,it will be seen that a plurality of primary cells, here represented asthree flashlight type batteries 33, 34 and 35, are connected in seriesto form a battery source for operating motor 10 and signal lamp 9. Thenegative side of this battery source 33-35 is connected to a ground buswithin the camera through a line 85, while the positive side of thebattery source 3335 is connected through a line 86 to adjustable contactmembers 20 and 21.

The circuit between contact member 20 and movable spring member 28 isbridged by a fixed resistor 87 which preferably is of a low resistancevalue. Resistor 87, for example, may be of the order of ohms. Thefunction of resistor 87 is to suppress sparking between fixed contact 20and movable contact 28 as the energizing circuit of motor 10 isalternately opened and closed during nor mal operation. Resistor 87 maynot be necessary if certain types of motors are employed, as for examplea motor adapted to operate on a very low battery voltage.

Flexible spring member 26, as shown in FIG. 1, is connected by a line 83to one terminal 89 of motor 1t) while another terminal 91 of motor it isconnected by a line 91 to spring leaf 43 of manually operated switch 46.Spring leaf 44 of manual switch 43 is grounded as shown at 92. Whenswitch spring 44 is moved from left to right as viewed in FIG. 1, switchspring 44 conductively engages spring 43 to close the described motorsupply circuit and start operation of motor 10. Further motion of switchspring 44 in the same direction brings insulated pin 48 into engagementwith spring 42 whereby force is applied to flex switch spring 42 intoconductive engagement with spring 41 to complete a signal circuit whichmay be traced from the positive side of battery source 33-35 throughline 86, thence through fixed contact 21, movable contact 29, flexiblespring 27, line 94 connecting signal control spring 27 with manualswitch spring 42, thence through switch spring 41, and finallyconnecting line 95 to one terminal 96 of signal lamp 9, the otherterminal 97 of which is grounded. Completion of the circuit justdescribed by complete closure of switch 46 energizes lamp 9. However, asthe motor circuit has also been energized by the operation of switch 49,motor 10 is started and governor 15 now raises insulated plunger 30 tofiex signal control spring 27 upwardly thus disengaging movable contact29 from fixed adjustable resistor at 87 whereby the current flow throughi 7' motor 15) when the supply circuit is open at contacts 20 and 28 maybe set at a value to maintain the desired speed of motor 10. Any slightdecrease in motor speed causes the centrifugal governor 15 to permitinsulated plunger 3% to retract sufficiently to re-establish contactbetween movable contact member 28 and fixed contact 20, therebyshortcircuiting resistor 87 and reapplying full potential from batterysource 33-35 to motor 1%.

The position of fixed contact 20 may be adjusted to provide for normalhunting operation of motor 10 between very close upper and lower limitsof speed by the alternate opening of contacts 20 and 28 at the upperlimit of tolerance and closing of these contacts at the lower tolerablelimit of speed. As the centrifugal governor 15 may exercise aconsiderable measure of control over speed changes of motor M, thecombined effect of centrifugal governor 15 and the electrical speedgoverning action of FIG. 1 provides an execeptionally well regulatedspeed control for motor 1% Still referring to FIG. 1, the operation ofthe signal control portion of this circuit will now be described ingreater detail. When the potential of battery source 3335 drops towardthe minimum potential required to maintain the operation of motor 10within the optimum speed range, the initial retardation of motor speedcauses the fiy weights 61 and 62 of centrifugal governor 15 to moveinwardly toward their axis of rotation about motor shaft 12, therebylowering insulated plunger 3% until movable contact 29 of signal controlspring 27 engages fixed contact 21 to complete the signaling circuitdescribed above and energize signal lamp 9. In normal operation, due tothe slight hunting action of centrifugal governor 15 in seeking tomaintain constant the speed of motor 10, the initial contact betweensignal control members 21 and 29 will be intermittent, as insulatedplunger 30 rises and falls slightly through the hunting action ofgovernor 15 at this speed. This intermittent closure of movable contact28 with fixed contact 21 produces a flashing indication in lamp 9 towarn the operator that motor speed has been reduced to a lower tolerablelimit. As the speed of motor 10 is reduced further, with further drop inpotential of battery source 3335, movable member 29 remains incontinuous engagement with fixed contact 21 to produce a constantindication in signal lamp 9 whereby the operator is informed that motorspeed has now dropped below the critical minimum necessary to assuremotion pictures of the desired quality.

Reference is now made to FIG. 2 of the drawings which represents analternative schematic circuit diagram whereby a signal indication ofdifferent characteristic may be obtained within the scope of theinvention. The elements of the circuit in FIG. 2 correspondsubstantially to the same elements shown in FIG. 1, the most significantdifference being in the connections to the signal control means. Asshown in FIG. 2, the signal control switch spring 27 in its idlecondition is dis-engaged from fixed signal contact 21. In the operationof the circuit of FIG. 2 it may be seen that when the springs of themanually operated starting switch 40 are all flexed into positions ofengagement, the motor energizing circuit is completed in exactly thearraova same manner as was described above in reference to FIG. 1. Therotation of centrifugal governor through normal operation of motor 10elevates insulated plunger 30 to engage flexible spring 27 wherebymovable contact 29 is brought into conductive engagement with fixedcontact 21 to complete the circuit through a line 95, manual switchsprings 41 and 42, and a line 94 whereby electrical energy from batterysource 33-35 is applied to signal lamp 9. In the normal operation of thecircuit of FIG. 8 this signaling circuit remains closed so long as motor10 is operating above a critical minimum speed, thereby producing acontinuous indication in signal lamp 9. As the speed of motor 10increases to the upper limit of its optimum range insulated pin 31operates on flexible spring 26 to open movable contact 28 fromconductive engagement with fixed contact whercby the motor energizingcircuit is opened, but the signal energizing circuit remains closedthrough contacts 21 and 29.

Thus it will be seen that in the circuit of FIG. 2 signal indicatinglamp 9 remains energized until the speed of motor 10 decreases to theminimum tolerable speed at which the contact between members 21 and 29is intermittently broken to produce a flashing signal indication by lamp9. Further reduction of the speed of motor in in the circuit of FIG. 2produces a continuous open circuit between contacts 21 and 29 therebyextinguishing lamp 9.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding descrip tion, are efiiciently attained and,since certain changes may be made in the above construction withoutdeparting from the scope of the invention, as for example the inventionmay be employed in direct current motor speed control and signalingsystems other than embodiment in a motion picture camera, it is intendedthat all matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

This application is a division of my co-pending application Serial628,283, filed December 14, 1956, for DC. Motor Speed Control andSignalling System, Particularly Designed for Motion Picture Cameras,which resulted in Patent 2,971,432, issued February 14, 1961.

I claim:

1. In a motion picture camera the combination with film trans-portmechanism, a source of direct current power, the voltage of which candrop below a predetermined critical value, a direct current motor whichslows up in drop of voltage of its power supply and is connected to saidfilm transport mechanism, and a supply circuit electrically to connectsaid power source to said motor for energizing the latter, of a speedcontrolled mechanism operable by said motor, switch means operable bysaid speed controlled mechanism and connected in said supply circuittemporarily to de-energize said motor at a predetermined criticalmaximum speed and permit energization thereof at speeds below thecritical maximum, electrical visual signal means visually to indicatemotor speeds below a predetermined lower limit, a signal circuit forenergizing said signal means from said power source, and switch means insaid signal circuit operable by said speed controlled mechanism at thepredetermined lower limit of motor speed for causing the signal means toindicate motor speeds at and below the lower limit of the motor s eed.

p 2. In a motion picture camera the combination with film transportmechanism, a battery source of direct current power the voltage of whichgradually drops with depletion, a direct current motor which slows upwith drop of voltage of its power supply and is connected to drive saidfilm transport mechanism, and a supply circuit electrically to connectsaid power source to said motor for energizing the latter, of a speedcontrolled governor operable by said motor, normally-closed switch meansoperable by said governor and connected in said motor supply circuit tomaintain closure of said circuit for energization of said motor atspeeds below a predetermined critical maximum and temporarily to breaksaid circuit at the critical maximum, an electrical visual signalvisually to indicate motor speeds below a predetermined lower limit, asignal circuit electrically to connect said power source to said visualsignal, and switch means in said signal circuit operable by saidgovernor at the predetermined lower limit of motor speed for causingsaid signal to indicate motor speeds at and below the lower limit of themotor speed.

3. An electric motor control and signal system comprising a batterysource of direct current power the voltage of which gradually drops withdepletion, a direct current motor rotatable at lower rates of speed withdrop in voltage of the source of power, a supply circuit electrically toconnect said power source to said motor for energizing the latter, aspeed controlled governor operable by said motor, normally-closed switchmeans operable by said governor and connected in said motor supplycircuit to maintain closure of said circuit for energization of saidmotor at speeds below a predetermined critical maximum and temporarilyto break said circuit at the critical maximum, an electrical visualsignal visually to indicate motor speeds below a predetermined lowerlimit, a signal circuit electrically to connect said power source tosaid visual signal, and switch means in said signal circuit operable bysaid governor at the predetermined lower limit of motor speed forcausing said signal to indicate motor speeds at and below the lowerlimit of the motor speed.

4. An electric motor control and signal system comprising a batterysource of direct current power the voltage of which gradually drops withdepletion, a direct current motor rotatable at lower rates of speed withdrop in voltage of the source of power, a supply circuit electrically toconnect said power source to said motor for energizing the latter, aspeed controlled governor operable by said motor, normally-closed firstswitch means operable by said governor and connected in said motorsupply circuit to maintain closure of said circuit for energization ofsaid motor at speeds below a predetermined critical maximum andtemporarily to break said circuit at the critical maximum, an electricalvisual signal visually to indicate motor speeds below a predeterminedlower limit, a signal circuit electrically to connect said power sourceto said visual signal, and a second switch means in said signal circuitoperable by said governor at the predetermined lower limit of motorspeed for causing said signal to indicate motor speeds at and below thelower limit of the motor speed, said first and second switch means eachcomprising a pair of cooperating stationary and movable contacts, themovable contacts being mechanically interconnected so that the actuationof one of said contacts by the speed controlled governor effects theactuation of the other movable contact.

References Cited in the file of this patent UNITED STATES PATENTS1,791,149 Sibley Feb. 3, 1931 1,843,922 Gay Feb. 9, 1932 2,079,539 Whiteet a1. May 4, 1937 2,278,573 Spear Apr. 7, 1942 2,850,653 Naul Sept. 2,1958 3,006,239 Smolar Oct. 31, 1961 3,038,110 Paist June 5, 19623,084,319 Hooljkamp Apr. 2, 1963

1. IN A MOTION PICTURE CAMERA THE COMBINATION WITH FILM TRANSPORTMECHANISM, A SOURCE OF DIRECT CURRENT POWER, THE VOLTAGE OF WHICH CANDROP BELOW A PREDETERMINED CRITICAL VALUE, A DIRECT CURRENT MOTOR WHICHSLOWS UP IN DROP OF VOLTAGE OF ITS POWER SUPPLY AND IS CONNECTED TO SAIDFILM TRANSPORT MECHANSIM, AND A SUPPLY CIRCUIT ELECTRICALLY TO CONNECTSAID POWER SOURCE TO SAID MOTOR FOR ENERGIZING THE LATTER, OF A SPEEDCONTROLLED MECHANSIM OPERABLE BY SAID MOTOR, SWITCH MEANS OPERABLE BYSAID SPEED CONTROLLED MECHANISM AND CONNECTED IN SAID SUPPLY CIRCUITTEMPORARILY TO DE-ENERGIZE SAID MOTOR AT A PREDETERMINED CRITICALMAXIMUM SPEED AND PERMIT ENERGIZATION THEREOF AT SPEEDS BELOW THECRITICAL MAXIMUM, ELECTRICAL VISUAL SIGNAL MEANS VISUALLY TO INDICATEMOTOR SPEEDS BELOW A PREDETERMINED LOWER LIMIT, A SIGNAL CIRCUIT FORENERGIZING SAID SIGNAL MEANS FROM SAID POWER SOURCE, AND SWITCH MEANS INSAID SIGNAL CIRCUIT OPERABLE BY SAID SPEED CONTROLLED MECHANISM AT THEPREDETERMINED LOWER LIMIT OF MOTOR SPEED FOR CAUSING THE SIGNAL MEANS TOINDICATE MOTOR SPEEDS AT AND BELOW THE LOWER LIMIT OF THE MOTOR SPEED.